Chemistry Reference
In-Depth Information
it is the largest volume polymer produced. Other ethylene derivatives, in
approximate order of volume of ethylene consumed, are ethylene dichloride,
ethylene oxide, and ethylbenzene.
Ethylene dichloride (EDC) is made by the direct chlorination of ethylene
[8] in the presence of a catalyst such as iron (III) chloride or copper (II)
chloride. EDC is also made by oxychlorination, a process where ethylene
reacts with HCl and oxygen in the presence of a catalyst, often copper (II)
chloride [9, 10]. The EDC is then converted to vinyl chloride, commonly
called vinyl chloride monomer (VCM) by a dehydrohalogenation reaction.
The VCM is then polymerized to polyvinyl chloride (PVC).
H
H
Cl
H
H
H
+Cl
2
CC
H
H
Cl
Direct chlorination
H
H
Cl
H
H
H
+ 2 HCl + 0.5 O
2
CC
+H
2
O
H
H
Cl
Oxychlorination
H
Cl
H
H
H
H
+HCl
CC
Cl
H
Cl
EDC
VCM
Dehydrohalogenation
The dehydrohalogenation of EDC to VCM is an endothermic reaction.
It is sometimes referred to as a thermal cracking reaction. The heat can be
supplied by the reactions that produce EDC. Both the direct chlorination and
the oxychlorination reactions are exothermic.
The production of VCM generates an equivalent of HCl. The oxychlori-
nation process provides an outlet for this HCl byproduct. In any large-scale
process it is critical to have an outlet for all byproducts. Although it is
performed in different reactors, the overall conversion of ethylene to VCM
can be written.
H
H
H
H
+ 0.5 O
2
+Cl
2
2
+H
2
O
2
CC
CC
H
Cl
H
H
Overall
An alternative process to VCM is from calcium carbide. This process is
used in China [11]. Calcium carbide, CaC
2
, is made by heating lime with
coal-derived coke. After treatment with water, acetylene is formed. The
acetylene is then reacted with HCl to produce VCM.
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